Floating roof storage apparatus for volatile liquids



March 14, 1944; w. G; LAIRD FLOATING ROOF S'I'ORA GE APPARATUS FORVOLATILE LIQUIDS INVENTOR Filed Aug. 6, 1940 0 m A m wym .6 M 8% V BBPatented Mar. 14, 1944 UNITED- STATES PATENT OFFICE FLOATING ROOFSTORAGE APPARATUS FOR VOLATILE LIQUIDS Wilbur G. Laird, Pleasantville,N. Y.

Application August 6, 1940, Serial No. 351,631 7 Claims. gol. 220-26)This invention relates to improvements in floating'roof storageapparatus for volatile liquids, especially such apparatus as is now usedfor the storage of relatively volatile petroleum products such asgasoline and. crude petroleum. More particularly the invention'relatesto improvements in floating roof tanks of relatively large diameters,usually in excess of 100 feet, employed for storing petroleum oils.

As far as known, the latest form of floating roof tank now used toaconsiderable extent in the petroleum industry comprises a large tank andfloating roof or deck of slightly smaller diameter than the inside ofthe tank resting directly on the liquid therein and floated by means ofpontoons. This type of roof is also provided with an elaborate resilientseal for closing the space between the roof and tank wall consisting ofvertical metal shoes bearing against the tank wall connected togetherand with the roof proper by a rubberized fabric material. The resilientseal is usually supported by means of hinged braces or supports fastenedto the floating roof proper.

Floating roofs of this type are very expensive, but at the same timeinclude no means for conserving -or saving the volatile gases and vaporsevolved from the stored liquid such as gasoline or crude oil. Theresilient seal doesnot prevent escape of gas and vapors, but merelyserves to prevent free access of the wind or air to the liquid betweenthe tank wall-and the floating roof proper. Furthermore, floating roofsof the type described are expensive to maintain because the upperportion of the tanks and all of the roof mechanism are open to theatmosphere and therefore trap'dust, water, sand, snow, etc. Theresilient seal operates against'a tank wall wetted by the stored liquidso that considerable contamination and obstruction isencounterecLespecially in crude oil storage tanks. I Furthermore, theinterior surface of the tank is subjected alternately to the liquid inthe tank and to the oxidizing effect of the atmosphere and corrosionoccurs, so that in the case of refined products contamination or changeof color may occur.

Having in mind the'elaboratenesahigh cost and disadvantages associatedwith the present type of floating roof storage apparatus, the primaryobject of the present invention is the provision of a floating roof tankprovided with a resilient seal, which will be relatively inexpensive,free from contaminating influences, and at the same time be eifectivefor the conservation of evolved gases and vapors.

According to the present invention, the imtilt provements in liquidstorage apparatus comprise in general a storage tank for example of thelarge cylindrical type, asheet metal roof adapted to be supported by theliquid in the tank and adapted to move relatively to the side wall ofthe tank as the liquid level in the tank varies, the floating roofincluding a metal roof plate preferably above the tank wall and adepending metal curtain wall or apron, for example, of the general shapeof the tank wall secured in fluid-tight manner to the roof plate nearthe periphery thereof inside the tank wall with its lower edge normallysealing in the, liquid in the tank, and a resilient annular closuremember or seal mounted in contact with the. tank wall, for example, ontop of the tank wall and adapted to enclose the space between thecurtain wall and tank wall to retard evaporation of and protect theliquid therebetween. 7

With such'an improved storage apparatus for liquids, to be described andelaborated more in detail hereinafter, the following improvements andadvantages over prior art storage tanks are attained:

1. Practically complete, elimination of contamination of the storedliquid from dust, dirt, water, etc.

2. Substantial savings in the cost of the floating roof.

3. Avoidance of contamination of the resilient closure seal by thestored liquid.

4. Avoidance of contact of the resilient closure seal with tank surfaceswetted by the stored liquid.

5. Reduction in the fire hazard.

6. Discharges tank atmosphere instead of drawing air into the tank areaas the tank is emptied. v

'7. Increased utility and reduced unit cost by providing full liquidcapacity storage as well as large gas and vapor storage andconservation.

Other features, improvements and advantages of the liquid storageapparatus of the present invention will be ap rent to those skilled inthe 'art "from the following'descriptlon of certain illustrated examplesmade in connection with the accompanying drawing in which:

Fig. 1 is an enlarged vertical transverse section through the upperportion of a cylindrical liquid storage tank illustrating one form ofthe invention.

Figs. 2, 3 and 4 are views similar to Fig. 1, illustrating further formsof the invention, except that Figs: 2 and 3 are'on a smaller scale andshow the lower portion of the tank.

rain water which is discharged outside the tank 1 7 wall In overextension IS. The floating roof also includes an annular or cylindricalsheet metal curtain wall or apron l8 which generally conforms to theshape of the wall I0 and extends slightly inside the wall l8, its loweredge normally sealing in the liquid 28 (Figs. 2 and 3) in the tank. Theroof plate l4, while preferably placed as shown, may be secured to thecurtain wall H3 at any desired level from about a foot above the loweredge of the curtain to the top, in line with the plate l6.

In the form of the apparatus shown in Fig. l, the space between the wallIll and the curtain I8 is enclosed by means of a resilient sealingmember 22 which is attached to the curb l2 by any suitable or well-knownmeans (not shown). The member 22 (as also members 30 and 34, (Figs. 3and 4) may comprise a mat seal of the type shown and claimed in theapplicants pending applicationSerial No. 332,659, filed May 1, 1940(which is not a gas-tight seal), or any other type of suitable sealingmember may be employed. The present invention is not concerned with thespecific type of seal used to enclose the space between the curtain I8and the wall II], but the mat seal described in the above-mentionedapplication is preferred. It is particularly applicable to the form oftank shown in Fig. 1 of the drawing, since the seal is inclined upwardlytoward the curtain wall [8 and serves to deflect or shed any extraneousmatter which is not diverted by the roof plate extension I8.

The curtain I8 is of sufiicient depth to seal in any liquid normallymaintained in the tank (Figs. 2 and 3), and at the same time keep theroof plate l6, and in the preferred form plate 14, above the wall [0 andsealing member 22. Curtain I8 is attached in fluid-tight manner to plateor sheet [4, and also preferablyfluid-tight to the annular plate I6.- 7

The modification of theinvention shown in Fig. 2 comprises, in additionto the elements shown in Fig. 1, an outside curtain or apron 24 attachedto the rim of the extension l6. This curtain 24 normally encloses asubstantial portion of the tank wall l8 and the sealing member 22, andthereby more perfectly prevents access of extraneous matter to theliquid in the tank. This curtain furthermore practically prevents theusual wind action. It will be noted that the curtain 24 is somewhatshorter than the curtain wall l8, to permit access to the sealing member22 by elevating the floating roof, so that the sealing member is exposedwhile the curtain wall I8 is still sealed in the liquid in the tank. Theelevation of the floating roof in this manner permits repair orreplacement of the sealing member 22.

Figs. 2 and 3 show the tank more completely than Figs. 1 and 4, andthese views include a portion of a bottom plate 26 on which is mountedlanding blocks 28 so that the curtain wall I8 will be supported slightlyabove the bottom of the tank, when the liquid is removed or the gasunder the roof plate I4 is removed sufliciently to let the roof curtainsettle to its lowermost position in the tank. In addition to the landingblocks 28 any suitable supporting means may be used to support the roofplate and take the weight of the roof. Such a structure is not shown,but is commonly employed in connection with floating roofs or decks.

Fig. 3 shows a further modification of the invention illustrated inFigs. 1 and 2 in which the annular resilient sealing member is mountedon the lower portion of the apron or curtain 24, so that it bearsagainst the outside of the tank wall [8 as the roof moves up and down inthe tank with the changes in liquid level or in the volume of gas insidethe curtain wall l8. The resilient sealing member as shown in Fig. 3comprises a mat or other form of resilient seal 30 fastened to thebottom portion of the curtain 24 by means of suitable clamping elements(not shown). The member 38 is illustrated as inclined downwardly(preferably) with respect to the curtain 24 against the tank wall It]and forced or held against the tank wall by means of suitable pivotedbracket levers 32, spaced at suitable intervals around the tank. Thesebracket levers 32 may be provided with weights 34, or springs or othersuitable means for holding the annular sealing member 30 in slidingcontact with the outside of the tank wall I8. The member 30 may beplaced horizontally or inclined upwardly if desired.

Fig. 4 shows a further modification of the floating roof tank in whichthe inside and outside curtains are employed as in Figs. 2 and 3, but inwhich the sealing member 34 is attached to the top of the tank wall I0and bears against the inside of the curtain 24. The annular sealingmember 34 may be inclined downwardly or upwardly from the tank wall I8and any suitable means (not shown) may be employed for causing themember to bear against the curtain 24. In many cases such a property(springiness and rigidity) may be inherent in the sealing member itself,so that outside springs or weighted brackets will be unnecessary.

In all modifications of the floating roof tank shown in Figs. 2, 3 and4, the curtain 24 is preferably secured in fluid-tight manner to theextension I6, and mat least Figs. 2 and 3, these curtains are preferablyshorter than the curtain wall I8. However, this may be unnecessary, asfor example when the curtain wall 24 is merely bolted to a flange on theextension I6 and can be readily removed.

The improved floating roof of the present in vention must of necessitybe held in substantially horizontal or level position, so that the loweredge of curtain I8 is substantially horizontal and the curtains l8 and24 move parallel with respect to the tank wall. The floating roof may bestabilized and maintained in this desired position by any suitable meansas for example by means of a cable or plurality of cables fastened tothe tank wall and/or bottom and the roof including curtains i8 and 24,in the various ways described in the applicants application, Serial No.329,875, filed April 16, 1940, for Storage tanks for oils and otherliquids. Alternatively, the floating roof may be held in a suitablehorizontal position by other guide means known in the art.

The liquid to be stored in the tank may be introduced thereinto orremoved therefrom by suitable piping or swing lines (not shown).Likewise suitable means (not shown) may be provided for removing vaporsand gases from under the floating roof or for supplying gas thereto,such means preferably including a swing line or equivalent for supplyingand removing gases from directly under the roof plate 14. However, a gasline terminating slightly above the top of the tank wall I within thecurtain wall I8 is suitable for supplying and removing gas. It will beapparent that the improved liquid storage tank of the present inventionmay be employed as a breather tank and connected to one or more storagetanks provided with fixed vapor-tight roofs. When the tank is connectedin this manner, gas and vapor from adjoining tanks, as well as thoseevolved from the liquid in the tank itself, will collect under thefloating roof within the curtain wall I8, for example, during the daytime, and at night when the tanks become cooler the floating roof willsupply gas to the outside tanks, and settle to a corresponding degree.

It will be apparent that the floating roof will move up and down in thetank as the liquid level therein so moves, and that it will also move inresponse to changes in the volume of gases under the roof within thecurtain wall l8. If gas is withdrawn abnormally, the roof may settle sothat the curtain wall rests directly on the landing blocks 28 and theliquid level rises inside the curtain wall i3 to the level outside.

The floating roof is also preferably provided with an automatic safetyvalve (not shown) of usual and well-known structure, adapted to preventthe creation of a Vacuum under the roof. Such a valve will also admitair under the roof when it is in a low position in the tank and when theoil or other stored liquid is being withdrawn. It is preferred howeverin such cases to supply outside gas under the floating roof to maintaina gas layer, so that the roof is at all times except when the tank isempty, supported by a gas layer above the liquid level within thecurtain I8. The safety valve referred to may also be arranged todischarge gas automatically in preference to permitting gas to bubblearound the lower edge of the curtain wall It as when too much gas issupplied to or evolved in the tank.

From the foregoing description of the various forms of apparatus of thepresent invention, it will be apparent that the applicant has provided afloating roof storage tank which is efiective for preventing excessivevapor losses, not only from the liquid stored therein, but also fromliquids stored in other closed tanks having their vapor spaces connectedwith the improved tank of the present invention. The floating roof isfurthermore arranged to trap and retain considerable and variablevolumes of gases and vapors, and thereby avoid the usual losses andprevent breathing of air into connected tanks such as those providedwith vapor-tight roofs. The annular resilient sealing means of thepresent invention is furthermore so arranged as to accomplish theresults and objects of the invention in connection with the use of theextension plate l6 and the curtain wall IE or curtain walls l8 and 24.

The improved liquid storage tank of the present invention greatlyreduces the hazard from fire in storing inflammable liquids because thefloating roof including the curtain 24 actually prevents air fromfilling the enclosed area of the of liquids and for reducing the lossdue to the evaporation of stored liquids such as petroleum products, anupright cylindrical storage tank of large diameter, a sheet metal roofadapted to be floated by the liquid in the tank and to move verticalllyrelative to the side wall of the tank as the liquid level in the tankvaries, said roof comprising a metal roof plate above and extending overthe tank wall and two depending annular metal curtains secured to theroof plate near the periphery thereof, one of said curtains being insidenear the tank wall secured in a fluid-tight manner to said plate andnormally extending into and sealing in the stored liquid in the tank.the other curtain being outside and near the tank wall and adapted toenclose a substantial portion of the heighth thereof, and a resilientannular closure member interposed between the tank wall and one of saidmetal curtains enclosing the space above the liquid around the insidecurtain, said closure member being adapted to permit the passage of gasinto and from said space but adapted to prevent the free circulation ofair into said space.

2. An apparatus for storing liquids as defined by claim 1 in which saidannular closure member is mounted between the tank wall and the outsidecurtain.

3. An apparatus for storin liquids as defined by claim 1 in which saidclosure member is fixed to the upper portion of the tank wall and bearsagainst one of said curtains in sliding contact therewith.

4. An apparatus for storing liquids as defined by claim 1 in which saidannular closure member is fixed to the lower portion of said outsidecurtain and bears against the outer side of said tank wall in slidingengagement therewith.

5. An apparatus for storing liquids as defined by claim 1 in which saidclosure member is fixed to the upper portion of the tank wall and bearsagainst one of said curtains in sliding contact therewith and in whichthe outside curtain is shorter than the inside curtain to an extentadapted to permit access to said closure member when the roof is insubstantially its maximum elevated position.

6. An apparatus as defined by claim 1 in which said annular closure isfixed to one part of the apparatus and in a position to avoid contactwith surfaces of the apparatus wetted by the liquid in the tank as .thelevel of the liquid in the tank varies.

7. A tank structure for storing volatile liquids and gases having a sidewall comprising an outer-lower stationary vertical annular wall sectionand a vertically movable section including an inner-upper annular wallsection of slightly smaller diameter than and spaced from said lowerwall section, a roof secured in fluid-tight manner to the top of theupper wall section, said upper wall section being open at, the bottomand of sufficient depth to extend from a point above the lower wallsection to normally seal in the liquid when stored therein, an annularshield at tached to the top portion of the upper wall section overlyingsaid stationary wall, and an annular closure member attached to theupper part of the. stationary wall section and mounted in slidingcontact with the outer surface of the other section enclosing the spacebetween said wall sections but adapted to permit the passage of gas toand from said space, thereby reducing evaporation of liquid between saidwall sections.

WILBUR G. LAIRD,

